In digital mobile radio systems, coded speech signals are transmitted over Raleigh fading channels where errors are due to adjacent and co-channel interference. To improve performance, Reed-Solomon (R-S) coding has been employed. This technique adds protection bits to the speech information bits, thereby providing the capability to correct errors within the individual R-S symbols. Each R-S symbol is transmitted as one or more radio symbols. In a typical implementation, a radio symbol consists of 2 bits, and each R-S symbol is comprised of 3 radio symbols. The radio symbol di-bits might, for example, be encoded using DQPSK modulation.
Information regarding the likelihood of each received radio symbol being correctly decoded is derived from the radio symbol decoding process. This information is used to predict those R-S symbols most likely to be in error, which are then marked as erased. This information regarding which R-S symbols are erased is used to increase the error correcting power of the R-S algorithm.
R-S coding schemes are described in a reference entitled "Error Control Coding: Fundamentals and Applications", Shu Lin, David J. Costello, Jr., Chapter 6 - BCH codes.